In recent years, vehicles mounted with navigation vehicle-mounted apparatus have rapidly been increased. The navigation vehicle-mounted apparatus holds a data base of a digital map and displays traffic jam or position of traffic accident on a map based on traffic jam information or traffic accident information provided from a traffic information center or the like, further, executes search for route by adding these information to conditions therefor.
Although the database of the digital map is formed by several companies in Japan, due to a difference in basic drawings and digitizing technology, the map data includes error and the error differs by the digital maps of the respective companies.
In the case of transmitting, for example, a position of traffic accident by traffic information or the like, when longitude and latitude data of the position is provided by itself, according to the vehicle-mounted apparatus, there is a concern that a position on a different road is identified as the position of the traffic accident depending on kinds of the data base of the digital map held.
In order to improve such inaccuracy of information transmission, conventionally, a node number is defined at a node such as a crossroads present in a road network, further, a link number is defined for a link representing a road between nodes, according to the digital map data base of the respective companies, respective crossroads and roads are stored in correspondence with node numbers and link numbers, further, in traffic information, a road is specified by a link number and a spot on the road is displayed by an expression method stating some meters from a head thereof.
However, a node number or a link number defined in a road network, needs to switch to a new number in accordance with newly laying or changing roads, further, when a node number or a link number is changed, the digital map data of the respective companies must be updated. Therefore, according to a system of transmitting position information of a digital map by using a node number or a link number, enormous social cost is required for maintenance thereof.
In order to improve such a point, the inventors of the invention have proposed, in Japanese Patent Application No. 214068/1999, a system in which in order to transmit a road position, an information providing side transmits “road shape data” comprising coordinate series indicating a road shape of a road section having a predetermined length including the road position and “relative position data” indicating the road position in the road section represented by the road shape data and a side of receiving the information specifies the road section on a digital map by executing map matching by using the road shape data and specifies the road position in the road section by using the relative position data, further, the inventors have proposed, in Japanese Patent Application No. 242166/1999, a system of also transmitting “additional information” such as kind of road, road number, a number of crossing links of nodes, angles of crossing links, name of crossroads and so on in a road section such that map matching on the receiving side can accurately be executed even when a transmission data amount of the “road shape data” is reduced, further, proposed a system of thinning the transmission data amount of the “road shape data” within a range by which erroneous matching on the receiving side is not brought about.
In this case, the map matching on the receiving side is carried out, for example, as follows.
As shown by FIG. 45, when as “road shape data” representing a road shape of a road bringing about traffic jam in section A through B, longitude and latitude data of spots P0 (x0, y0), P1 (x1, y1), . . . , Pk (xk, yk) are transmitted as follows,                (x0, y0) (x1, y1) . . . (xk, yk),as shown by FIG. 44, the receiving side selects roads included in a range of error centering on spot P0 (x0, y0) by using map data read from a digital map data base of its own as candidates and narrows down candidates therefrom by using transmitted “additional information”. When a single candidate is narrowed down, positions most proximate to (x0, y0) and (xk, yk) of the road are calculated and the section is defined as a road section represented by “road shape data”.        
When the single candidate is not narrowed down and roads Q and R remain as candidates, positions Q0 and R0 on the respective candidate roads most proximate to P0 (x0, y0) are calculated and distances between P0 through Q0 and P0 through R0 are calculated. The operation is executed for respective points P1 (x1, y1) . . . , Pk (xk, yk) A road section minimizing a value produced by adding square means of the distances from respective points P0, P1, . . . , Pk is calculated and the road section is specified by a method of determining the road section as a road section represented by the “road shape data”.
The traffic jam section of A through B is specified based on the transmitted “relative position data” with a position of starting the road section calculated from the “road shape data” as onset.
When position information on a digital map is transmitted by traffic information or the like, it is necessary to transmit data such that a correct position can be recognized by a counterpart in a short period of time.
Further, as a case of transmitting position information on a digital map, there is assumed a case of transmitting information of a disaster site in mountains or accident at rivers and therefore, it is also necessary to transmit a map shape of other than roads or position information of a spot other than roads.
The invention responds to such problems and it is an object thereof to provide a method of transmitting position information of a digital map for further improving a method of transmitting position information of a digital map by using “shape data” specifying a map shape on the digital map and “relative position data” specifying a relative position in the map shape specified by the “shape data”, capable of transmitting a position on the digital map efficiently and accurately, further, capable of transmitting also position information other than a road shape of a spot on a road, further, provide an apparatus used therefor.